1. Field of the Invention
The present invention relates to a liquid crystal display, and more particularly, to a liquid crystal display which is capable of reducing power consumption and improving display quality.
2. Discussion of the Related Art
Recently, various flat panel display devices have been developed to reduce weight and volume which are disadvantages of a cathode ray tube. These flat panel display devices may be, for example, a liquid crystal display, a field emission display, a plasma display panel, a light emitting device, and the like.
The liquid crystal display, among the flat panel display devices, includes a liquid crystal panel including a plurality of liquid crystal cells arranged in matrix form and a plurality of control switches for switching video signals to be supplied respectively to the liquid crystal cells, and a backlight unit for supplying light to the liquid crystal panel. The liquid crystal panel is adapted to control transmittance of the light supplied from the backlight unit to display a desired image on a screen.
Recently, backlight units have become smaller, thinner and lighter. According to this trend, there have been proposed backlight units using light emitting diodes (referred to hereinafter as LEDs) which are advantageous in terms of power consumption, weight, brightness, etc., instead of fluorescent lamps.
FIG. 1 schematically shows the configuration of a liquid crystal display of the related art using an LED backlight unit.
Referring to FIG. 1, the conventional liquid crystal display comprises a liquid crystal panel 2 having liquid crystal cells formed respectively in areas defined by n gate lines GL1 to GLn and m data lines DL1 to DLm, a data driver 4 for supplying analog video signals to the data lines DL1 to DLm, a gate driver 6 for supplying scan signals to the gate lines GL1 to GLn, a timing controller 8 for controlling the data driver 4 and gate driver 6 and generating a dimming signal DS using input data RGB, and an LED backlight unit 10 for turning on a plurality of LEDs in response to the dimming signal DS to irradiate light to the liquid crystal panel 2.
The liquid crystal panel 2 includes a transistor array substrate and a color filter array substrate bonded to face each other, a spacer for keeping a cell gap between the two array substrates constant, and a liquid crystal filled in a liquid crystal space provided by the spacer.
The liquid crystal panel 2 further includes thin film transistors (TFTs) formed respectively in the areas defined by the n gate lines GL1 to GLn and the m data lines DL1 to DLm, and liquid crystal cells connected respectively to the TFTs. Each TFT supplies an analog video signal from a corresponding one of the data lines DL1 to DLm to a corresponding one of the liquid crystal cells in response to a scan signal from a corresponding one of the gate lines GL1 to GLn. Each liquid crystal cell can be equivalently expressed as a liquid crystal capacitor Clc because it is provided with a pixel electrode connected to the corresponding TFT, and a common electrode facing the pixel electrode with a liquid crystal interposed therebetween. This liquid crystal cell further includes a storage capacitor Cst for maintaining an analog video signal charged on the liquid crystal capacitor Clc until a next analog video signal is charged thereon.
The timing controller 8 arranges data RGB externally inputted thereto suitably for the driving of the liquid crystal panel 2 and supplies the arranged data to the data driver 4. Also, the timing controller 8 generates data control signals DCS and gate control signals GCS using a dot clock DCLK, a data enable signal DE, and horizontal and vertical synchronous signals Hsync and Vsync externally inputted thereto, and applies the generated data control signals DCS and gate control signals GCS to the data driver 4 and gate driver 6, respectively, to control the driving timings thereof.
The timing controller 8 also generates a dimming signal DS for control of the LED backlight unit 10 using the input data RGB.
The gate driver 6 includes a shift register for sequentially generating scan signals, or gate high signals, in response to the gate control signals GCS from the timing controller 8. This gate driver 6 sequentially supplies the gate high signals to the gate lines GL of the liquid crystal panel 2 to turn on the TFTs connected to the gate lines GL.
The data driver 4 converts data signals Data supplied from the timing controller 8 into analog video signals in response to the data control signals DCS from the timing controller 8 and supplies analog video signals of one horizontal line to the data lines DL at intervals of one horizontal period in which each scan signal is supplied to each gate line GL. That is, the data driver 4 selects gamma voltages having certain levels based on gray scale values of the data signals Data and supplies the selected gamma voltages to the data lines DL1 to DLm. At this time, the data driver 4 inverts the polarities of the analog video signals to be supplied to the data lines DL1 to DLm in response to a polarity control signal POL.
The LED backlight unit 10 includes an LED array 12 including a plurality of LEDs, and an LED controller 14 for turning on the LEDs in response to the dimming signal DS from the timing controller 8.
The LED controller 14 generates a pulse width modulation (PWM) control signal Vpwm corresponding to the dimming signal DS and supplies the generated PWM control signal Vpwm to the LED array 12.
The LED array 12 is disposed to face the rear surface of the liquid crystal panel 2, and includes a plurality of red, green and blue LEDs arranged repetitively.
Each LED is turned on in response to the PWM control signal Vpwm supplied from the LED controller 14 to emit light to the liquid crystal panel 2.
This liquid crystal display of the related art using the LED backlight unit converts input data RGB into analog video signals and supplies the converted video signals to the respective data lines DL synchronously with the supply of a scan signal to each gate line GL to drive the liquid crystal cells. Also, the liquid crystal display turns on a plurality of LEDs with a PWM control signal Vpwm corresponding to a dimming signal DS based on the input data RGB from one predetermined dimming curve to irradiate light to the liquid crystal cells. Therefore, the liquid crystal display controls transmittance of light irradiated from the LED backlight unit 10 through the liquid crystal cells driven by the analog video signals to display an image corresponding to the input data on the liquid crystal panel 2.
However, the liquid crystal display using the LED backlight unit is disadvantageous in that it cannot partially emphasize the brightness of an image displayed on the liquid crystal panel 2 using the LED backlight unit because it generates the dimming signal DS based on the input data RGB from one predetermined dimming curve.
In other words, in the case where the input data has a high average picture level (referred to hereinafter as an APL) as in a dimming curve REF1 having an abrupt gray level variation, as shown in FIG. 2, an image outputted to the liquid crystal panel is mostly present in a bright area. In this case, when the dimming signal is supplied to the LED backlight unit using any one of the dimming curve REF1 or dimming curve REF2, the LED backlight unit may scarcely dim, resulting in a reduction in power consumption reducing effect. Particularly, in the case where the dimming signal is based on the dimming curve REF2 having a slow gray level variation, a side effect such as darkening or flashing of the screen may occur depending on the APL.